Solution mining, also referred to as in-situ leach mining, is a commonly used method for extracting water-soluble salts such as sylvite (i.e., potash) halite (i.e., sodium chloride), and sodium sulfate. It is also used as a method for producing underground storages cavities for liquid hydrocarbons, compressed natural gas, and waste products. In its most basic form, solution mining requires a cased and cemented borehole, generally comparable to gas or oil wells, which connects a surface plant to the area of water-soluble salt formation (i.e., a salt deposit). Water-based fluids or solvents are injected through the borehole and salt is dissolved from the salt formation to form brine. The brine is then brought back up to the surface for processing. Solution mining is often used in situations where the deposits are too deep or too thin for conventional mining techniques, and solution mining generally creates minimal surface disturbance and little waste compared to conventional mining. Other advantages of solution mining include the fact that impurities in the mined salt can be readily removed from the brine, which allows for production of high-grade salt for other uses, including food, chemical, and pharmaceutical manufacturing. Additionally, any impurities (i.e., insolubles) are readily disposed of by reinjecting them into the cavern. Furthermore, brine is easily transportable and is often times the required form of raw material in some chemical manufacturing processes.
Effective solution mining requires the creation and maintenance of a stable cavern that will remain intact over the course of the leaching period, typically 2-5 years. During the leaching period, the shape of the cavern can be influenced by several parameters, such as the leaching rate, the amount of water or solvent injected, the depths of the leaching equipment, and the duration of the leaching intervals. Often times the roof or upper portion of the cavern is protected by a pad of crude oil. This oil pad is applied to ensure that leaching with, for example, injected water, occurs horizontally only, rather than vertically into the cavern roof. If water is allowed to leach vertically, high concentrations of salt will not be achieved, and the cavern roof would be more likely to collapse.
The use of a pad of oil to mitigate the risks associated with the creation and maintenance of cavity control is quite expensive. One way to reduce this expense would be to reduce the amount of oil required for effective cavity control. For example, one such method could involve the use of emulsions, in particular, reverse emulsions. Emulsions are mixtures of two or more liquids in which particles or droplets of a nonpolar liquid (e.g., oil) are dispersed in a polar medium (e.g., water). Reverse emulsions are typically mixtures of droplets of a polar liquid in a nonpolar medium. The stability of an emulsion or a reverse emulsion depends on the liquids used to create it. Emulsion stability refers to the ability of an emulsion to resist change in its properties and internal-phase bubble size over time. In order to counteract the tendency of emulsions and reverse emulsions to become destabilized, an appropriate surface active agent (i.e., surfactant) or emulsifier, can be used. Generally, surfactants or emulsifiers increase the kinetic stability of an emulsion so that the size of the droplets does not change significantly over time.
Given the widespread use of solution mining, there remains a need to develop efficient and economical materials and methods to maintain cavity control during the leaching process, which can last as long as five years. More specifically, there remains a need to develop materials and methods to reduce the volume of oil required to create the oil pad at the roof of the cavern in order to prevent vertical leaching and cavern collapse.